In the recovery of oil from oil-containing formations, it usually is possible to recover only minor portions of the original oil in place by the so-called primary recovery methods which utilize only the natural forces present in the formation. Thus, a variety of supplemental recovery techniques have been employed in order to increase the recovery of oil from subterranean formations. Since it is known that the viscosity of oil decreases markedly with an increase in temperature, thermal recovery methods such as in-situ combustion and steam flooding have been employed.
In the in-situ combustion process an oxygen containing gas is introduced into the formation and high temperature combustion of the reservoir oil is initiated and maintained. The oxygen reacts with the residual oil laid down during the process to generate heat and, as a result, carbon oxides are formed. In this process the heat of combustion is given up to the reservoir oil, thereby lowering the viscosity of the oil over a substantial portion of the formation and enhancing the recovery of the oil. Because of high temperature, the reaction rate is high. Another recovery technique is the low temperature oxidation process which is similar to the high temperature oxygen combustion process except that a lower temperature (between 250.degree.-600.degree. F.) is maintained so that oxygen is chemically uptaken by the oil with little, if any, formation of carbon oxides like CO.sub.2, CO, etc. With reaction rate slower than for combustion, less oxygen is consumed. For a given amount of oxygen injected, greater area of the reservoir being heated when compared to the high temperature oxygen combustion process. However, an adverse effect of low temperature oxidation is the increase in oil viscosity, which decreases oil mobility.
These thermal recovery methods have not been successful all the time. In the high temperature oxygen combustion and low temperature oxidation processes much heat is left behind in the swept formation and most of this goes to waste. On the other hand, the steam flood process is often limited by heat losses in the injected steam at the surface, in the wellbore, and in the formation. As a result, the high quality steam process originally intended is often down graded to a low quality steam process, or even to a hot waterflood. This heat loss is large when the steam is applied in a thermal recovery process in a deep reservoir.
There is therefore a present need for compensating for such heat losses in the thermal oil recovery processes. The present invention is particularly directed to compensating for the heat losses in the steam flood process by the in-situ generation of heat for the purpose of maintaining the high steam quality desired for enhancing oil recovery during such a steam flood process.